Re: [PATCH 5/5] KVM: vmx: use MSR_IA32_TSX_CTRL to hard-disable TSX on guest that lack it

From: Eduardo Habkost
Date: Wed Nov 20 2019 - 21:29:10 EST

On Mon, Nov 18, 2019 at 07:17:47PM +0100, Paolo Bonzini wrote:
> If X86_FEATURE_RTM is disabled, the guest should not be able to access
> MSR_IA32_TSX_CTRL. We can therefore use it in KVM to force all
> transactions from the guest to abort.
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>

So, without this patch guest OSes will incorrectly report "Not
affected" at /sys/devices/system/cpu/vulnerabilities/tsx_async_abort
if RTM is disabled in the VM configuration.

Is there anything host userspace can do to detect this situation
and issue a warning on that case?

Is there anything the guest kernel can do to detect this and not
report a false negative at /sys/.../tsx_async_abort?